If the co-pilot of the Germanwings flight that crashed in the French Alps on Tuesday deliberately flew the jet into a deadly descent, as prosecutors assert, it would certainly be a rare event. But not nearly as rare as most people think.

This was the sixth time since 1982 that a commercial pilot has committed suicide/murder by aircraft, taking planeloads of passengers with him — and that's a short count.

It doesn't include the mysterious disappearance last year of Malaysia Airlines Flight 370, which appears to have been flown off course. Nor does it count a troubled flight engineer's unsuccessful attempt to kill three pilots on a FedEx Boeing 707 in 1994.

The pattern has largely gone unnoticed, but it is striking, particularly in the similarities between the Germanwings crash and the ill-fated flight of EgyptAir 990 in 1999.

Family members of a victim lay tributes to the victims in front of a stele, a stone slab erected as a monument, set up in the area where a Germanwings aircraft crashed in the French Alps, in Le Vernet, France, on March 28. Claude Paris, AP

A man prays during a religious ceremony for victims of a Germanwings flight that crashed in the French Alps, killing all 150 aboard, on March 28, 2015 at Notre-Dame-du-bourg cathedral in Digne-les-Bains, near the site of the crash. Jeff Pachoud, AFP/Getty Images

Flowers, candles and photographs decorate a monument dedicated to the victims of Germanwings flight 4U9525 on March 26 in front of the mountain where the plane crashed in Le Vernet, France. A Germanwings flight from Barcelona to Dusseldorf crashed in the French Alps on March 24 killing all 150 people on board. Patrick Aventurier, Getty Images

A search and rescue worker passes debris and wreckage at the crash site of the Germanwings Airbus A320 in the French Alps near Seyne. The aircraft with 150 people on board crashed March 24 during a flight from Barcelona to Duesseldorf, Germany. Guillaume Horcajuelo, European Pressphoto Agency

Pupils gather in Haltern, Germany, March 25 at the Joseph-Konig High School to pay tribute to 16 students and two teachers from the school who were on Germanwings Flight 9525. Sean Gallup, Getty Images

A photograph of victims is displayed at a makeshift memorial at Joseph-Koenig High School in Germany. Sixteen students and two teachers from the school were on Germanwings Flight 9525. Sean Gallup, Getty Images

A photograph by the French Interior Ministry shows wreckage and debris at the crash site of the Germanwings Airbus A320 on the French Alps near Seyne. F. Balsamo, French Interior Ministry via European Pressphoto Agency

A student lights a candle in front of the Joseph-Konig-Gymnasium in Haltern, western Germany. A Germanwings plane that crashed in the French alps was transporting 16 children and two teachers from Haltern. Martin Meissner, AP

A man who appears to have been waiting for the arrival of Germanwings Flight 9525 covers his face at the airport in Duesseldorf, Germany. A Germanwings Airbus A320 passenger jet carrying 144 passengers and six crew crashed in the French Alps on a flight from Barcelona to Duesseldorf. Frank Augstein, AP

Queen Letizia of Spain, left, and her husband, King Felipe VI, listen as French President Francois Hollande addresses the media at the Elysee presidential palace in Paris. The royal couple canceled their first state visit to France after word of the plane crash. Bertrand Guay, AFP/Getty Images

French President Francois Hollande speaks during a visit at the League Against Cancer in Paris. The French leader warned that there may be no survivors from the Germanwings plane crash. Thibault Camus, AP

This Feb. 24, 2014, file photo shows a Germanwings Airbus A320 in front of the terminal at Koeln-Bonn airport in Cologne, Germany. A Germanwings passenger jet carrying 148 people has crashed in the French Alps. Oliver Berg, AP

The EgyptAir jetliner was en route from New York to Cairo when the captain left the cockpit to go the bathroom, just as the Germanwings pilot did. Within seconds, the co-pilot disengaged the autopilot, pushed the yoke forward and took actions to bring the aircraft down, as he quietly repeated, "I rely on God."

The pilot rushed back in — unimpeded by the impregnable locks put on cockpit doors after 9/11 — and fought the co-pilot for control, too late. The Boeing 767 crashed into the ocean 60 miles off Nantucket, killing all 217 aboard. While Egypt blamed mechanical failure, U.S. investigators had no doubt: The crash was deliberate.

Similar tragedies have occurred in Indonesia, Japan, Morocco and Namibia.

Given the time span of three decades and the fact that 87,000 flights fly safely in the USA every day, that's not cause for alarm. But neither is it reason to look away. There are safety options to consider.

Reenforced cockpit doors, which can be securely locked from inside, are the most effective security measure since the Sept. 11 hijackings, but they backfired for Germanwings. The pilot, locked out by the co-pilot, could be heard banging furiously to get in as the jet descended.

U.S. rules requiring two people in the cockpit at all times might have prevented the crash. On Thursday, some international airlines adopted the procedure, and others would do well to follow.

And what about regular mental health assessments for pilots? Commercial pilots in the U.S. must undergo medical exams annually or, after 40, twice a year. Exams include a general look at their mental state, but no formal psychological assessment.

Pilots and crews clearly assess each other because their lives depend upon it. They may be in the best position to notice and report a mental health problem. Given the number of crashes, though, professional psychological assessments might be needed.

Suicide and mass murder, which is what really happened on Germanwings, aren't easily prevented. Just ask those who've groped for years to stop the endless succession of mass killings by deranged gunmen in America. You can't stop them all. But you can stop some.

The pattern of crashes repeated in the Alps on Tuesday argues that the threat is overdue for some attention.